// Copyright 2025 International Digital Economy Academy
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

///|
priv struct Cons[A] {
  content : A
  mut next : Cons[A]?
} derive(Eq)

///|
// Invariant:
// - length == 0 <=> first is None && last is None
struct T[A] {
  mut length : Int
  mut first : Cons[A]?
  mut last : Cons[A]?
}
